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Partial Evidence to Recommendations for use of
chikungunya vaccines among persons in U.S.
territories at risk for chikungunya virus
transmissionNational Center for Emerging and Zoonotic Infectious Diseases
Dr. Lyle Petersen
Director, Division of Vector -Borne Diseases
Advisory Committee on Immunization Practices meeting
June 26, 2025
•Two licensed chikungunya vaccines
-Live attenuated vaccine licensed in November 2023 for use in persons aged ≥18
years (manufactured by Valneva)
-Virus -like particle vaccine licensed in February 2025 for use in persons aged ≥12
years (manufactured by Bavarian Nordic)
•Chikungunya Vaccines Work Group formed in May 2022
-Approved recommendations exist for use of vaccines in travelers and laboratory
workers
-Recent topic under discussion has been use of chikungunya vaccines in persons in
U.S. territories and states at risk for chikungunya virus transmissionBackground
Evidence to Recommendations ( EtR) for use of
chikungunya vaccines among persons in U.S. territories
at risk for chikungunya virus transmission:
Public health problem and value of a vaccine
EtR framework
EtR Domain Question
Public health problem •Is the problem (chikungunya) of public health importance?
Benefits and harms•How substantial are the desirable anticipated effects of CHIK -VLP?
•How substantial are the undesirable anticipated effects?
•Do the desirable effects outweigh the undesirable effects?
•What is the overall certainty of this evidence for the critical outcomes?
Values•Does the target population feel the desirable effects are large relative to
the undesirable effects?
•Is there important variability in how patients value theoutcomes?
Acceptability •Is the intervention acceptable to keystakeholders?
Resource use •Is the intervention a reasonable and efficient allocation ofresources?
Equity •What would be the impact of the intervention on health equity?
Feasibility •Is the intervention feasible to implement?
Public Health Problem
Question: Is the problem of public health importance?
Key related questions include:
•Are the consequences of the problem serious?
•Are a large number of people affected by the problem?
•Is the problem related to emerging diseases …. or epidemic potential?
Chikungunya virus transmission
Countries and territories with current or past transmission of chikungunya virus
Globally, ~620,000 cases
reported in 2024 but likely
underestimate
Outbreaks can be
large and explosive
•One-third to three -
quarters of po pulation
affected
•Substantial morbidity
•Stresses healthcare
capacity
No highly effective alternatives to vaccination for
disease control
Acknowledgement: Claudia Colon -Burgos & Coral Rosado- Santiago, CDC Dengue Branch•Mosquito prevention and control
measures
-Use of insect repellent challenging as
requires daily use during outbreaks
-Source reduction important but difficult to remove enough water -
holding containers where mosquitoes
lay eggs
•Other prevention measures have
had variable impact
•Fever and joint pain
-Arthralgia often severe and can be
debilitating
-Multiple joints involved, most
commonly hands and feet
•Other symptoms include
headache, myalgia, fatigue, rash,
abdominal pain, and vomiting
•No anti -viral treatment
-Supportive managementImpact of acute illness
Image above from : https://www.paho.org/en/topics/chikungunya
•Rare serious complications (e.g., cardiac,
renal, ocular, neurologic illness)
•Hospitalization rate ~3%
•Case fatality rate: 0.01% –0.5%
•Serious outcomes mostly in older adults and young infantsImpact of disease: severe presentations
Images from : https://www.paho.org/en/topics/chikungunya
Impact of disease: Arthralgia that persists or recurs
•Most patients have arthralgia that resolves in
7–10 days
•Arthralgia sometimes persists or relapses with
other symptoms e.g., fatigue
Impact of disease: Arthralgia that persists or recurs
Based on recent meta -analysis (Lindsey N. Chronic arthralgia after chikungunya. US Advisory Committee on Immunization Practices meeting, June 2023)*
*Rates likely overestimated as background rate of arthralgia in the population could not be taken into account51% 3 months
post -infection12 months
post -infection
38%Acute
illness
100%
Chikungunya previously documented in five U.S. territories
and affiliated states
•Puerto Rico
•United States Virgin Islands (USVI)
•American Samoa
•Federated States of Micronesia
•Marshall Islands
Reported chikungunya cases by month of illness onset,
Puerto Rico, 2014 –2015*
050010001500200025003000
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
2015 2014*Cases reported to Puerto
Rico Department of Health
Reported chikungunya cases by year and case status,
Puerto Rico, 2014 –2020
0200040006000800010000
2014 2015 2016 2017 2018 2019 2020Probable
Confirmed
Last laboratory -confirmed
symptomatic clinical case
•Seroprevalence study indicated
~30% population infected during
outbreak1
•Based on 30% seroprevalence
rate, ~1 million persons infected,
and 65% –85% of chikungunya
virus infections being symptomatic
-~650,000 –850,000 clinical
cases Estimated number of clinical cases in Puerto Rico
chikungunya outbreak
1. 1,268 of 4,035 participants (Adams LE at al, PLoS NTD 2022);
Estimated 650,000– 850,000
clinical cases during the outbreak
in Puerto Rico*
*Based on ~30% post -outbreak population seroprevalence (Adams LE at al, PLoS NTD 2022) and 65% –85% of infections being symptomatic
Estimated hospitalizations and deaths in
chikungunya outbreak in Puerto Rico, 2014 –2015
19,500– 25,500 hospitalizations* 65-85 deaths#
*Based on 3% hospitalization rate#Based on 0.01% case -fatality rate
•Federated States of Micronesia (Yap State): 2013– 2014
•USVI: 2014– 2015
•American Samoa : began June 2014
•Marshall Islands: began February 2015Chikungunya in other U.S. territories and affiliated states*
*ACIP presentation, June 2024 (https://www.cdc.gov/acip/downloads/slides -2024- 06-26-28/03- Chikungunya -Hills -508.pdf)
Summary: Is chikungunya of public health importance
in U.S territories with risk of transmission?
1. Acute illness can be severe, hospitalizations can occur (particularly in
vulnerable groups), and arthralgia can persist for months or years
2. Timing of next outbreak is unknown but is likely to evolve rapidly and might affect a substantial proportion of population
3. Outbreaks can impact health services through patient loads and staff absenteeism
4. No highly effective control measures exist apart from vaccination
Question: Is the problem of public health importance?
□No
□Probably no
□Probably yes
□Yes
□Varies
□Don’t know
Values and preferences
1. Target population perception of value
Do potential vaccine recipients feel that the desirable effects are large relative
to undesirable effects?
2. Uncertainty around target population perception of value
Is there important uncertainty about, or variability in, how much people value the main outcomes? Values and preferences
Value of a chikungunya vaccine for residents of Ponce,
Puerto Rico: Study methods
•Data collected as part of larger study mos quito -borne disease study*
•Chikungunya component conducted in 2024, ~10 years after chikungunya
outbreak in Puerto Rico
•Included 2,437 individuals or caregivers aged 1– 56 years
•Asked basic question about interest in vaccination with hypothetical chikungunya vaccine if free of charge or at ≤$10, and reasons if not
interested or unsure
*Adams LE et al. PLoS Negl Trop Dis 2022
If there was an approved chikungunya vaccine available
in Puerto Rico, free of charge or at low cost ($ 10 or less), would you get vaccinated (N=2,437)?
No Unsure Yes71%23%
7%Participants who had
completed at least some
higher education or had no
history of chikungunya
more likely to respond
“no” or “don’t know”*
*Preliminary analyses
What are the reasons why you would not be interested
or are not sure if you would be interested in getting vaccinated against chikungunya?*
*Could select ≥1 reason0510152025303540Percentage
•Part of larger population -based household study
•Conducted soon after end of outbreak in June 2015
•Included 966 participants aged 1– 91 years
•Subjects or caregivers questioned about interest in
receiving a hypothetical chikungunya vaccine
•Estimates calibrated to age and sex of USVI population Value of chikungunya vaccine in United States Virgin Islands
Population of 106,405 in 2010
Curren EJ et al. Am J Trop Med Hyg 2022
010203040506070Adjusted proportions with 95% CI
Vaccine interest56% interested in vaccineVaccine interest among participants (adjusted proportion)
25%
19%
Interested (n=520) Not interested (n=258) Unsure (n=188)
010203040506070Adjusted proportions with 95% CI
Vaccine interest56% interested in vaccineVaccine interest among participants (adjusted proportion)
25%
19%
Interested (n=520) Not interested (n=258) Unsure (n=188) Persons aged ≥40 years less
likely to be interested vs. persons aged 0 –19 years
Reasons for potential lack of interest in vaccine among
those not interested or uncertain about vaccination (N=446)
•Wanting more safety information: 47% (95% CI: 41– 52%)
•Lack of concern for getting disease: 16% (95% CI: 13– 20%)
•Already had chikungunya disease: 10% (95% CI: 7– 13%)
•Majority of participants indicated interested in a hypothetical vaccine at time
surveys implemented
-Higher interest in Puerto Rico (71%) v s. USVI (56%) possibly influenced by timing of
surveys in relation to outbreaks and general vaccine uptake differences in two
territories
•For respondents potentially not interested in vaccine, key concern was
needing a better understanding of vaccine safety
-Will be important to provide resources and education on vaccine safety if
chikungunya vaccine introducedSummary
Question: Does the target population feel that the
desirable effects of vaccination are large relative to undesirable effects?
□No
□Probably no
□Probably yes
□Yes
□Varies
□Don’t know
Question: Is there important uncertainty about or
variability in how much people value the main outcomes?
□Important uncertainty or variability
□Probably not important uncertainty
or variability
□No important uncertainty or variability
□No known undesirable outcomes
Update on safety of live attenuated chikungunya
vaccine in older personsNational Center for Emerging and Zoonotic Infectious Diseases
Serious adverse events in older persons
•Status as of April 2025 ACIP meeting
-6 serious adverse events (SAEs) occurred in US persons aged ≥65 years during 2024*
-Discussed at ACIP meeting on April 16 and CDC determined age ≥65 years is
precaution to vaccination with live attenuated chikungunya vaccine
•Updates since April 2025 ACIP meeting
-In the 3 weeks following ACIP meeting, 11 additional SAEs reported internationally in
persons aged 62 –89 years, most with underlying medical conditions#
-European Medicines Agency recommended temporary pause in vaccine use in ages ≥65 years (May 7)
-FDA and CDC recommended temporary pause in the live, attenuated vaccine use in ages ≥60 years to allow investigations of reports (May 9)
¥
-Awaiting outcome of FDA investigations
*Reported through Vaccine Adverse Events Reporting System (VAERS) #Mainly from Reunion where large outbreak occurring
¥FDA and CDC Recommend Pause in Use of Ixchiq (Chikungunya Vaccine, Live) in Individuals 60 Years of Age and Older While Postmarketing Safety Reports are Investigated | FDA
ACIP Chikungunya Vaccines Work Group
Arboviral Diseases Branch, CDC
•Sarah Guagliardo
•Susan Hills
•Erin Staples
Dengue Branch, CDC
•Laura AdamsAcknowledgements
For more information, contact CDC
1-800- CDC- INFO (232 -4636)
TTY: 1 -888- 232- 6348 www.cdc.gov
The findings and conclusions in this report are those of the authors and do not necessarily represent the official position of the Centers for Disease Control and Prevention.